RE: About ppp_receive()

Hi Zhenhua Zhang, Zhenhua wrote: > Hi Steven, > > Steven wrote: >> Hi, >> >> In function ppp_receive, we first check the protocol type of this >> frame like: >> >> guint16 protocol = ppp_proto(buf); >> >> and here we assumed the length of the protocol field is 16 bits, >> but in RFC 1661, the protocol field should be one or two octets. >> >> "The Protocol field is one or two octets, and its value identifies >> the datagram encapsulated in the Information field of the packet." >> >> why we given the assumption that protocol field is 16 bit length? > > First I am not ppp expert. :-). > > If you take look at pppd source code, main.c, get_input() also > always fetch two bytes 'protocol' for struct protent as well. > > Can you give a case we failed in our ppp stack? If you interested in this topic, you can reference RFC 1661 Section 6.5, which said -------------- This Configuration Option provides a method to negotiate the compression of the PPP Protocol field. By default, all implementations MUST transmit packets with two octet PPP Protocol fields. PPP Protocol field numbers are chosen such that some values may be compressed into a single octet form which is clearly distinguishable from the two octet form. This Configuration Option is sent to inform the peer that the implementation can receive such single octet Protocol fields. ------------- In our current source code, because we only negotiate two configuration options - REQ_OPTION_MRU and REQ_OPTION_ACCM. so it's okey for our PPP stack.

But some carriers, like China Telecom or Sprint Network etc, will support the full configuration options(Magic-Number,Protocol-Field-Compression,Address-and-Control-Field-Compression), So if PFC option is used ,our code will got wrong with ppp_receive().

We should first check if PPP protocol field is compressed or not, and then get the right protocol value to form a 16 bits protocol field, and pass this value to the rest functions. Because of my company's security policy ,I can't provide a patch for this issue. But i can provide a method for doing this. Here it is.

First byte of PPP protocol field may be compressed, if the LS bit is 1 then this indicates that the upper protocol us compressed, because the upper byte should be even, the lower byte should be odd. >> In CDMA 2000 environment, just as the Sprint Network, PPP should >> support a compressed protocol field. Is there anything difference >> between GSM and CDMA? >> >> B.R >> >> Steven B.R Steven --------------------------------------------------------------------------------------------------- Confidentiality Notice: The information contained in this e-mail and any accompanying attachment(s) is intended only for the use of the intended recipient and may be confidential and/or privileged of Neusoft Corporation, its subsidiaries and/or its affiliates. If any reader of this communication is not the intended recipient, unauthorized use, forwarding, printing, storing, disclosure or copying is strictly prohibited, and may be unlawful.If you have received this communication in error,please immediately notify the sender by return e-mail, and delete the original message and all copies from your system. Thank you. --------------------------------------------------------------------------------------------------- _______________________________________________ ofono mailing list ofono(a)ofono.org http://lists.ofono.org/listinfo/ofono